1. Field of the Invention
The present invention relates to a structure of an exhaust system for a vehicle, and more particularly, to a structure of a dual exhaust system for a CDA engine capable of reducing low frequency noise by avoiding an outlet pipe resonance at the time of a CDA mode by connecting between two main mufflers through a connecting pipe and equipping a valve in one of the outlet pipes to open and close the one outlet pipe.
2. Description of Related Art
Recently, as environmental issues are increased, an environmental problem due to an excessive emission of exhaust gas of a vehicle has emerged and consumers are highly likely to prefer a high fuel efficiency vehicle due to the rise in oil prices. Therefore, various technologies for improving fuel efficiency of a vehicle and an engine output have been developed.
Various technologies, such as a variable induction system (VIS) which changes a length or a cross sectional area of an intake manifold in response to an air suction resistance changed depending on a rotating region of an engine, a variable valve timing (VVT) which controls an opening and closing timing and a lift of a valve depending on a rotating area of an engine, a variable valve lift (VVL) which controls a lifting height of a valve, and a cylinder deactivation (CDA) which converts a part of engine cylinders into a non-operation/full operation depending on a driving condition for the purpose of improving fuel efficiency, have been developed and applied to a vehicle.
Among those technologies, the CDA engine device an engine which deactivates some of all the cylinders at the time of braking or cruise and an operation of a fuel supply and intake/exhaust valve stops at a deactivated cylinder side.
A maximum output of a vehicle engine is required only when a vehicle is accelerated or goes up a ramp. Therefore, when the vehicle is driven even by a partial output of the engine, all the cylinders are not necessarily ignited, and as a result, fuel may be saved.
For example, in the case of a vehicle in which a six-cylindered engine is equipped, there is no need to generate power by operating all the cylinders in a braking or low idle condition or a low load condition while in the driving state. Therefore, power is generated by deactivating the operation of three cylinders and activating the operation of only the remaining three cylinders.
As illustrated in FIGS. 1A and 1B, a structure of a dual exhaust system for a CDA engine is a structure in which two inlet pipes 1 branched from an engine of a vehicle are connected to two main mufflers 2 and two outlet pipes 3 are connected from the two main mufflers 2.
As illustrated in FIG. 1A, when the engine of the vehicle is in a general mode, exhaust gas is emitted to both sides through the two main mufflers 2 and as illustrated in FIG. 1B, when the engine of the vehicle is in the CDA mode, the exhaust gas is emitted to only one side through one main muffler 2.
The structure of a dual exhaust system for a CDA engine according to the related art is a structure in which in the CDA mode, only one main muffler is used and the other main muffler is deactivated, and therefore has noise reduction performance which is more deteriorated than the case of using the two main mufflers.
The CDA engine consumes less fuel than a typical engine and therefore has excellent fuel efficiency, but has some of the cylinders which are not ignited, and therefore changes main components of the engine noise to increase noise in a low frequency range.
The main component of the engine noise device a value obtained by dividing an explosive number of an engine by an engine RPM, which is represented by the following Equation.
[Equation]Main Component of Engine Noise=Explosive number of Engine/Engine RPM
That is, in the case of the vehicle in which the 6-cylindered engine is equipped, in a general mode in which all of the 6 cylinders are operated, the noise component corresponding to C3 (6/2=3) in the following Table 1 forms the main component of the engine noise and in the CDA mode in which only the three of the six cylinders are operated, the noise component corresponding to C1.5 (3/2=1.5) forms the main component of the engine noise.
TABLE 1C1.5C3C4.5C61,000 rpm 25 Hz 50 Hz 75 Hz100 Hz6,000 rpm150 Hz300 Hz450 Hz600 Hz
Therefore, in the CDA mode in which only the three of the six cylinders are operated, the low frequency noise component (noise component corresponding to C1.5 among the main components of the engine noise) which is little generated in a general mode is additionally generated and then combined with a low frequency resonance mode of the existing outlet pipe, which may have a bad effect on the vehicle noise.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.